1. Field of the Invention
The present invention generally relates to a common rail such as a high pressure fuel manifold or a block rail in a diesel internal combustion engine.
2. Description of the Prior Arts
Conventionally as a common rail of this kind,for example, as shown in FIG. 7, there is known a common rail oft a type in which each of a plurality of pieces of boss portions 31-4 provided, at intervals, at a peripheral wall portion in an axial direction of a circular pipe on a side of a main pipe rail 31 comprising the circular pipe, is perforated with a branch hole 31-2 having a pressure receive seat face 31-3, communicating with a communication path 31-1 of the main pipe rail 31 and opened outwardly, a pressing seat face 32-3 constituted by a connection head portion 32-2 on a side of an injection pipe 32, is brought into contact and engaged with pressure receive eat face 31-3 on the side of the main pipe, rail 31 and is fastened to connect thereto by screwing a fastening outer screw nut (or cap nut) 33 previously integrated to the side of the injection pipe to the boss portion 31-4 in accordance with pressing operation under a neck of the connection head portion 32-2 in the drawing, notation 32-1 designates a flow path of the branch pipe 32 and notation 34 designates a fastening sleeve washer.
In such a common rail, the injection pipe arranged the common rail and a nozzle, is shortened such that a sufficient amount can be injected into a combustion chamber without causing pressure lose in the common rail and in consideration of convenience in view of piping. However, even in such a short injection pipe, when a valve is closed after fuel injection, pressure variation is caused in the injection pipe. The pressure variation becomes pulsation and reaches the communication path 31-1 of the main pipe rail 31, further passes through the branch hole 31-2 and influences on an injection pipe of a successive cylinder and accordingly, there poses a problem in which fuel can not be injected stably.
Although as a countermeasure thereagainst, the pressure variation can be reduced by, for example, increasing an inner diameter of the main pipe rail 31 to thereby increase an inner volume of the pipe, there causes a drawback that the pulsation is transmitted fastly. Hence, there has been developed a method of providing an orifice in a common rail in order to restrain pulsation lowly and retarding propagation thereof. With regard to the method, there are known a method for providing orifice function by further reducing a diameter of the branch hole 31-2 provided at the boss portion 31-4 of the main pipe rail 31 and a method in which as shown by FIG. 8, a metal ring member (barrel) 35 with an orifice having a pressing seat face 35-1 and a pressure receive seat face 35-2, is interposed between the pressure receive seat face 31-3 of the branch hole 31-2 and the injection pipe connection head portion 32-2 at a portion of the branch hole 31-2 of the main pipe rail 31, and pulsation can be restrained lowly and propagation can be retarded by either of the methods. However, according tot the method, of providing the orifice function by further reducing the diameter of the branch hole, since repeated pressure at high pressure is applied to the branch hole portion, a portion thereof having the thinnest thickness is equal to or large than 7 mm, further, there is carried out fabrication at a portion which is deep from an end face of the boss portion and accordingly, there is a difficulty in which fabrication of a hole having a slender diameter is not easy in forming the orifice. Further, according to the method of interposing the metal ring member (barrel) 35 with an,orifice between the pressure receive seat face 31-3 of the branch hole 31-20 and the injection pipe connection head portion 32-2, by axial force by a single piece of the fastening outer screw nut 33 integrated to the side of the injection pipe, two locations, that is, two locations of a portion of sealing the pressure receive seat face 31-3 of the branch hole and the pressing seat face 35-1 of the metal ring member 35 and a portion of sealing the pressure receive seat face 35-2 of the meal ring member 35 and the pressing seat face 32-3 of the injection pipe connection head portion, are sealed and therefore, there is a drawback of insufficient stability of seal.
It is an object of the invention to provide,a common rail carried out in order to resolve the above-described conventional problem and capable of injecting fuel stably by restraining pulsations lowly and retarding propagation by providing an orifice pipe in a branch pipe to thereby achieve orifice function.
In order to achieve the above-described object, according to an aspect of invention, there is provided a common rail which is a common rail constituted by providing a branch hole communicating with a communication path and having a pressure receive seat face opened outwardly at each of a plurality of pieces of integrated type boss portions or separate type boss portions provided at a peripheral wall portion in an axial direction of a main pipe rail having the communication path at inside thereof in an axis core direction thereof while maintaining intervals there between, bringing and engaging a pressing seat face portion constituted by a connection head portion having a flow path communicating with the communication path and provided at an end portion thereof in contact with the pressure receive seat face and fastening to connect the pressing seat face portion thereto in accordance with pressing operation under a neck of the connection head portion by screwing a fastening nut, wherein the common rail is constituted by providing an orifice pipe having ant outer diameter at least the same as or smaller than a hole diameter of the branch hole in the branch hole.
Further, as the orifice, pipe, there can be used a constitution in which the orifice pipe includes a thick-walled flange portion having a diameter larger than a flow path diameter of an injection pipe at an end portion of the injection pipe on a side of the connection head portion, or a constitution in which the orifice pipe comprises a pipe member made of a hard metal and a ring made of a soft metal having a diameter larger than a flow path diameter of the injection pipe outwardly fitted to an end portion of the pipe member on a side of the connection head portion or a constitution in which the orifice pipe comprises an inner pipe made of a hard metal and an outer pipe made of a soft metal having a thick-walled flange portion having a diameter larger than the flow path diameter of the injection pipe at the end portion of the injection pipe on the side of the connection head portion.
That is, the invention is constituted such that by providing the orifice pipe in the branch hole of the main pipe rail, the orifice pipe serves :as an orifice and does not influence seal performance and fuel can be injected stably by restraining pulsation lowly and retarding propagation. Further, in the case of the orifice pipe having the flange portion, when the flange portion is soft, axial force of a nut is not cancel thereby and seal face pressure is not lowered.
Further, as means for fixing the orifice pipe, according to the invention, there can be used means of press-fitting, calking, shrinkage fitting, chill fitting, soldering, bonding or the like.